In an apparatus including a power supply circuit for converting an ac input voltage into a predetermined output voltage and an output operation circuit for performing a predetermined operation by adopting the output voltage as input, stresses greater than at normal times are imposed on circuit components such as IGBT, capacitor, reactor or the like in the case where a voltage abnormality such as voltage distortion, three-phase unbalance, instantaneous voltage drop, instantaneous interruption of service or the like occurs in a voltage supplied to the power supply circuit, or in the case where an improper voltage is applied due to improper wiring, which may cause problems such as damage to components, or the like.
Accordingly, circuit components of a power supply circuit have conventionally been protected by detecting abnormalities of a current flowing in semiconductor switching devices such as IGBT, transistor or the like as an instantaneous overcurrent when it exceeds a certain threshold and a dc voltage as an overvoltage when it exceeds a certain threshold, respectively, and in response to this detection, stopping a switching operation of the power supply circuit or turning off a main relay.
Further, there has been presented actively detecting a power-supply voltage abnormality by providing means for detecting supply voltage waveforms, and stopping a driving power or making an appropriate correction at the occurrence of abnormality, to thereby allow a protecting operation and prevent the occurrence of component damage or abnormal sound (cf. Patent document 1).
Patent document 1: Japanese Patent Application Laid-Open No. 2003-169481